function removeClass(el,cls){
  var classes=el.className.split(/\s+/);
  if(classes.indexOf(cls)!==-1){
    classes.splice(classes.indexOf(cls),1);
  }
  el.className=classes.join(' ');
}
function hasClass(el,cls){
  var classes=el.className.split(/\s+/);
  if(classes.indexOf(cls)!==-1){
    return true;
  }
  return false;
}
function addClass(el,cls){
  if(!hasClass(el,cls)){
    el.className+=' '+cls;
  }
}
